the kitchen sink faucet (single handle), when turned to the hot side, has a very, very low flow of water. I checked the valve handle and it is fully open.
The faucet, I would guess, is about 7 or 8 years old. Do I need to replace the inner stem or is it something else?

I am guesiing that this is the only fixture that has low flow. I would first check to see if the supply line on the hot side is kinked. If it isfine then I would check the faucet cartridge (whaT you are calling the stem) for debris. I

If there is a flexible supply hose connected to the faucet for the hot water, check it for interior swelling. A very simply way to do that is to switch the hot and cold hoses and see if the cold is then slow.

Shut off hot water valve and remove supply line. Slowly open valve to test for pressure, if not pressure, remove valve stem and see what you find wrong there. If pressurized, check supply line, blowing it to make sure is open. If line is open then you have to deal with the faucet.

I tried your suggestions and found that the valve was the culprit. it turned freely and worked somewhat but when i removed it, there was a rubber stopper that had separated from the handle. I replaced the valve and all is flowing normal. thanks for your help everyone.